Animal production, a major component of the U.S. agricultural economy, is at risk because of both real and perceived environmental problems. Dramatic advancements are required to protect the environment, save this vital industry, and maintain food security. Municipal and agricultural waste disposal is a major problem. For agricultural animals, the animals are confined in high densities and lack functional and sustainable treatment systems. Confined livestock produce approximately 1329 million pounds of recoverable manure phosphorus annually with about 70% (approximately 925 million pounds) in excess of on-farm needs. This livestock production system was developed in the early and mid 20th century prior to the current trend in high concentrated livestock operations. One of the main problems in sustainability is the imbalance of nitrogen (N) and phosphorus (P) applied to land (Edwards, D. R., and T. C. Daniel, Bioresource Technology, 41: 9-33 (1992)). Nutrients in manure are not present in the same proportion needed by crops, and when manure is applied based on a crop's nitrogen requirement, excessive phosphorus is applied resulting in phosphorus accumulation in soil, phosphorus runoff, and eutrophication of surface waters (Sharpley et al., J. Soil Water Conserv, 62: 375-389 (2007); Heathwaite, L., et al., J. Environ. Qual., 29: 158-166 (2000); Sharpley, A., et al., J. Environ. Qual., 29: 1-9 (2000); Edwards and Daniel, Bioresource Technology, 41: 9-33 (1992)).
Phosphorus build up in soils to excessively high levels due to animal manures often results in eutrophication and pollution of surface waters due to intense application of animal manures to land (Edwards and Daniel, 1992; USEPA, 1992; Heathwaite et al., 2000; Sharpley et al., 2000). This is a national problem affecting dairy, poultry, and swine production systems. Consequently, a substantial amount of manure phosphorus needs to be moved at least off the farms and some needs to be transported longer distances beyond county limits to solve accumulation and distribution problems of this nutrient (USDA-ERS, Agricultural Outlook, September 2000, p. 12-18). Manure nutrients in excess of the assimilative capacity of land available on farms are an environmental concern often associated with confined livestock production. The ability to extract-phosphorus from manure will be critical to poultry and livestock producers to accomplish manure utilization through land application without elevating soil phosphorus levels when land is limited. In addition, the aspect of phosphorus reuse is becoming important for the fertilizer industry because the world phosphorus reserves are limited (Smil, V., Annu. Rev. Energy Environ., 25(1):53-88 (2000)). According to the Potash and Phosphate Institute, the United States annual consumption of inorganic phosphorus for crop production is about 3700 million pounds (Potash and Phosphate Institute, 2002, Plant nutrient use in North American agriculture, Technical Bulletin 2002-1). On the other hand, for the U.S. as a whole, confined livestock produces about 1,329 million pounds of recoverable manure phosphorus annually with about 70% (about 925 million pounds) in excess of on-farm needs (Kellogg, R. L., et al., Manure nutrients relative to the capacity of cropland and pastureland to assimilate nutrients: Spatial and temporal trends for the United States, NRCS and ERS GSA Publ. No. nps00-0579. Washington, D.C., 2000). Therefore, reuse of phosphorus recovered from animal waste could substitute about 25% of the phosphorus now obtained from mining.
Farmers obtain nutrients for their crops from inorganic commercial fertilizers and from organic sources such as animal manure and biosolids from wastewater treatment plants. Inorganic nitrogen and phosphorus compounds are water soluble and readily available to plants. Most organic nutrient sources contain both inorganic forms of nutrients and forms that must first be mineralized or decomposed to become available to plants. The movement of nitrogen and phosphorus through soil are different. If nitrogen is converted to the highly water soluble nitrate-nitrogen form, and it is not used during plant growth, it can move through the soil-water system and be vulnerable to leaching into groundwater. Soil amended with large quantities of organic or inorganic phosphorus may generate significant amounts of soluble phosphorus that can be readily transported by surface and subsurface runoff and groundwater leachate.
A further problem with the management of human and animal waste is the loss of nutrients. Phosphates and nitrates are fundamental nutrients which determine the possibility for plant and animal life to occur. They are taken up by plants and the plants are eaten by animals. Subsequently they should return to the soil as manure in a normal agricultural cycle, but in the present situation in most cases they end up washed into the sea, whether they are simply dumped in a river or go through a municipal wastewater treatment
The lack of closure of the nutrient cycle is a major environmental problem, especially in the case of phosphates which, at present, are considered a mineral resource to be extracted. Excess of phosphates in the seas causes eutrophication. The depletion of the mineral phosphate resources is a problem which will become important in the near future (Scrivani et al., Solar trough concentration for fresh water production and waste water treatment, Desalination, 206: 485-493 (2007))
In livestock operations, the crop acreage is typically calculated to allow for uptake by the crops of the applied nitrogen from the soil, thus minimizing movement of nitrogen in ground and surface water beyond the farm's boundaries.
Unlike carbon and nitrogen, phosphorus cannot volatilize from the system. Crops typically take up less phosphorus from the soil than that applied in the manure because the acreage has been calculated for nitrogen removal, which requires less acreage. The soil absorbs phosphorus but over time reaches saturation. Additional application of phosphorus can cause release of phosphorus to surface waters beyond the farm's boundaries, risking oxygen depletion of water organisms. Measures for reducing phosphorus content of manure must be considered.
Phosphorus inputs accelerate eutrophication when it runs off into fresh water and has been identified as a major cause of impaired water quality (Sharpley et al., 2000). Eutrophication restricts water use for fisheries, recreation, industry, and drinking due to the increased growth of undesirable algae and aquatic weeds and resulting oxygen shortages caused by their death and decomposition. Also many drinking water supplies throughout the world experience periodic massive surface blooms of cyanobacteria. These blooms contribute to a wide range of water-related problems including summer fish kills, unpalatability of drinking water, and formation of trihalomethane during water chlorination. Consumption of cyanobacteria blooms, or water-soluble neuro- and hepatoxins released when these blooms die, can kill livestock and may pose a serious health hazard to humans. Recent outbreaks of the dinoflagellate Pfiesteria piscicida in near-shore waters of the eastern United States also may be influenced by nutrient enrichment. Although the direct cause of these outbreaks is unclear, the scientific consensus is that excessive nutrient loading helps create an environment rich in microbial prey and organic matter that Pfiesteria and menhaden (target fish) use as a food supply. In the long-term, decreases in nutrient loading will reduce eutrophication and will likely lower the risk of toxic outbreaks of Pfiesteria-like dinoflagellates and other harmful algal blooms. These outbreaks and awareness of eutrophication have increased the need for solutions to phosphorus run-off.
Past research efforts on phosphorus removal from wastewater using chemical precipitation have been frustrating due to the large chemical demand and limited value of by-products such as alum sludge, or because of the large chemical demand and huge losses of ammonia at the high pH that is required to precipitate phosphorus with calcium (Ca) and magnesium (Mg) salts (Westerman and Bicudo, Tangential flow separation and chemical enhancement to recover swine manure solids and phosphorus, ASAE Paper No. 98-4114, St. Joseph, Mich., ASAE, 1998; Loehr et al., Development and demonstration of nutrient removal from animal wastes, Environmental Protection Technology Series, Report EPA-R2-73-095, Washington, D.C., EPA, 1973). Other methods used for phosphorus removal include flocculation and sedimentation of solids using polymer addition, ozonation, mixing, aeration, and filtration (see U.S. Pat. No. 6,193,889 to Teran et al). U.S. Pat. No. 6,153,094 to Craig et al. teaches the addition of calcium carbonate in the form of crushed limestone to form calcium phosphate mineral. The patent also teaches adsorbing phosphorus onto iron oxyhydroxides under acidic conditions.
Continuing efforts are being made to improve agricultural, animal, and municipal waste treatment methods and apparatus. U.S. Pat. No. 5,472,472 and U.S. Pat. No. 5,078,882 (Northrup) disclose a process for the transformation of animal waste wherein solids are precipitated in a solids reactor, the treated slurry is aerobically and anaerobically treated to form an active biomass. The aqueous slurry containing bioconverted phosphorus is passed into a polishing ecoreactor zone wherein at least a portion of the slurry is converted to a beneficial humus material. In operation the system requires numerous chemical feeds and a series of wetland cells comprising microorganisms; animals, and plants. See also U.S. Pat. Nos. 4,348,285 and 4,432,869 (Groeneweg et al); U.S. Pat. No. 5,627,069 to Powlen; U.S. Pat. No. 5,135,659 to Wartanessian; and U.S. Pat. No. 5,200,082 to Olsen et al (relating to pesticide residues); U.S. Pat. No. 5,470,476 to Taboga; and U.S. Pat. No. 5,545,560 to Chang.
One of the main problems in sustainability of poultry production is the imbalance between nitrogen and phosphorus in the waste (Edwards and Daniel, USEPA, 2001). Nutrients in manure are not present in the same proportion needed by crops. The mean N:P ratio in manure is generally lower than the mean N:P ratio taken up by major grain and hay crops (USDA, 2001). To solve the problem of a phosphorus buildup in soil and increased potential for phosphorus losses through runoff and subsequent eutrophication of surface waters, efforts are being made to immobilize phosphorus or find alternative uses for poultry litter such as burning and gasification and transport to agricultural lands with low levels of phosphorus. Current methods for handling phosphorus in waste include immobilization, see for example U.S. Pat. No. 6,923,917; gasification (Sheth, A. C., and A. D. Turner, Trans. ASAE, 45(4):1111-1121 (2002)), precipitation, see U.S. Pat. No. 7,005,072; litter transport to agricultural lands with low levels of phosphorus (Jones, K., and G. D'Souza, Agric. Resour. Econ. Rev., 30(1):56-65 (2001); Kelleher, B. P., et al., Bioresour. Technol., 83(1) 27-36 (2002); Keplinger, K. O., and L. M. Hauck, Impacts of livestock concentration and application rate restrictions on manure utilization, ASAE/CSAE Meeting Presentation, Paper No. 042204. ASAE, St. Joseph, Mich., 2004); anaerobic digestion by combustion (USDOE-NREL, 2000, Biomass co-firing: A renewable alternative for utilities, NREL/FS-570-28009, DOE/GO-102000-1055, U.S. Department of Energy, National Renewable Energy Laboratory), etc.
While various systems have been developed for treating solid animal waste for the removal of phosphorus, there still remains a need in the art for a more effective treatment system for the phosphorus. The present invention, different from prior art systems, provides a system for extracting phosphorus from solid animal manure using a selective extraction and subsequent recovery.